There is currently a trend in replacing the traditional light bulb with more energy efficient alternatives. Florescent light sources also in forms resembling the traditional light bulb have been shown and are often referred to as compact fluorescent lamps (CFLs). As is well known, all florescent light sources contain a small amount of mercury, posing problems due to the health effects of mercury exposure. Additionally, due to heavy regulation of the disposal of mercury, the recycling of florescent light sources becomes complex and expensive.
Accordingly, there is a desire to provide an alternative to florescent light sources. An example of such an alternative is provided in WO 2005074006, disclosing a field emission light source containing no mercury or any other health hazardous materials. The field emission light source includes an anode and a cathode, the anode consists of a transparent electrically conductive layer and a layer of phosphors coated on the inner surface of a cylindrical glass tube. The phosphors are luminescent when excited by electrons. The electron emission is caused by a voltage between the anode and the cathode. For achieving high emission of light it is desirable to apply the voltage in a range of 4-12 kV.
The field emission light source disclosed in WO 2005074006 provides a promising approach to more environmentally friendly lighting, e.g. as no use of mercury is necessary. However it is always desirable to improve the design of the lamp to prolong the life time, and/or to increase the luminous efficiency of the lamp.